The invention relates generally to a device for generating data for dot patterns for forming characters and images and more particularly to a device for forming dot patterns for characters and images of both standard sizes and enlarged sizes without magnifying stepped portions of the characters and images that are intended to simulate smooth lines.
A conventional serial printer includes a plurality of ink nozzles, exothermic elements or impact wires n a printing head mounted on a reciprocating a carriage. A conventional laser printer transfers toner images to a recording medium by exposing a photosensitive drum with laser beams. Both conventional serial and laser printers form characters and graphics by aggregating hyperfine dots so that the observer perceives individual dots as continuous smooth lines. Accordingly, these devices require a dot pattern data generator for converting character code signals into dot patterns.
A typical dot pattern data generating device includes a storage device for storing the characters specified by character code signals in the form of dot data which is expressed by either the existence or the non-existence of dots corresponding to the character codes in a form to be readable in accordance with character code data.
In some instances, both standard size characters and large size characters are required to be printed in the same document. To provide a printer that can meet this requirement, it is common to store the large size character dot pattern data in the same device that stores the standard size dot data. However, storing large size character dot pattern data, which are infrequently used, in the same device for storing the normal size character dot data increases the cost of the storage device because the storage circuit must have a larger storage capacity.
To solve this problem, the so-called outline font method was proposed. The standard size character pattern data is not stored in the form of dot data but as outline data representing outlines of the standard size characters. To print enlarged characters, the outline data is enlarged to the desired size by an arithmetic unit during printing and the outline data is converted into dot data. This method is advantageous because the amount of data to be stored is smaller and the storage capacity can be reduced.
Unfortunately, the outline font method requires a large number of arithmetic operations to convert the outline data into dot data. This is detrimental because either this method increases printing time or it requires a high speed arithmetic unit, which can be costly. To solve these problems, a method of using a standard size character dot pattern and multiplying each dot into a plurality of dots by a multiplying factor was proposed. For example, in the case of a 4-fold enlargement, each dot of the standard size dot pattern is converted into four dots.
To visualize how this method works, the printing area can be represented by a matrix of squares that contain or do not contain dots. Diagonal lines and curves are represented by a stepped pattern of squares containing dots. To yield a four-fold enlargement, each square, blank or filled is bisected in both the horizontal and vertical directions to yield four squares ((2.times.2)-fold enlargement). When the pattern is converted to an image, the "quarter size" squares are formed to be the size of the original squares. To yield a 9-fold enlargement, each original square is converted into nine squares.
This method is advantageous because the dot patterns of enlarged characters can be generated at a high speed by simple arithmetic operations without increasing the storage capacity. However, this method also has drawbacks. Curved or oblique appearing lines of the original dot pattern are actually formed in a stepped pattern, but the "steps" are too small to be noticeable. When performing this character enlargement method, the stepped portions shaping the oblique lines are enlarged by the same multiplying factor. This results in decreased character quality because the stepped nature of the lines becomes more noticeable.
To solve this problem, it was proposed to modify the method to smooth the oblique line patterns by increasing or decreasing the dots which form the oblique lines of the character dot patterns. Japanese Patent Application Laid-Open No. 60-014286 describes a dot pattern data generating device which incorporates a function to modify the dot patterns into smooth configurations. Each of the dots representing the standard character dot pattern is multiplied into a corresponding number of dots by the multiplying factor and a dot pattern for enlarging the character is generated.
A storage device stores all the patterns of the stepped portions of the oblique lines which are shaped when being enlarged and modifies the patterns in a dictionary format. The dot pattern outlines of the enlarged characters which are generated in the previous step are cut out and replaced with the corresponding modified patterns.
This method also has drawbacks. It requires substantial time until optimal modified patterns are output because of the necessity for reading the modified patterns by a so-called mask pattern matching retrieval method in which the outline dot patterns are compared with mask patterns prepared beforehand. In addition, the shape balance of the character as a whole is lost due to undesirable partial swelling or thinning of character portions, although smooth outline patterns can be attained because of the uniform replacement with the modifying patterns.
Conventional dot pattern data generators therefore have inadequacies due to these shortcomings. Accordingly, it is desirable to provide a improved dot pattern data generator which avoids the shortcomings of the prior art and yields properly shaped smooth characters and images of various sizes.